Any good tips on repairing cracks in plastic?

[silverback]

I think my bike is possessed. Now, I have a star shaped fatigue crack extending from one of the bolts in the right fairing. Any good tips on repair?

Thanks.

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[Bust]

ABS Plastic is a real bitch when it starts cracking like that.
The plastic washers between the bolt head and fairing do a decent job but if you get ham fisted on the tightening somethings gonna give eventually.

I've had limited success plastic welding on the backside of the crack.. You build it up and then grind it back down to fit mount area.
And hope you don't warp the damned stuff in the process. Hopefully somebody has a better method, as I'm willing to learn.

[Name Etc.]

Bike bandit has pretty good fiche and decent prices... They repair will look like new also.

[bluesdog]

I've had good results with devcon plastic repair -- http://www.devcon.com/products/products ... r%E2%84%A2" onclick="window.open(this.href);return false;

First I reduce the thickness of the area by using a small grinder, (dremel or similar).

Next, if the damaged area is at all structural, I cut a small bit of fibreglass cloth to reinforce the repair. For small, cosmetic repairs the fibreglass is optional

Then I mix the devcon epoxy, apply a thin layer to the repair area, then press the fibreglass on, and finish with another coat of epoxy, working it firmly into the weave of the fibreglass.

Once set, grind the area back to original thickness, but now it will be stronger than the original abs, and the cracks will be functionally repaired. Make sure you contour the repaired area as closely as possible to the original.

There may still be hairline cracks visible on the finished side, but they are now only on the surface. These can be sanded, filled and repainted, but usually you'll have to repaint a much larger area in order to blend well into the surrounding finish.

The devcon plastic repair epoxy is one of those products that seems to work as advertised

For hairline cracks you can also use a solvent, such as Dichloromethane, which temporarily melts the plastic, in order to 'weld' it together. Note this does not make the area any stronger. Be careful with any plastic solvent, as they tend to be somewhat toxic.

Pretty much any repair will have to be repainted to totally eliminate visible signs of the cracks

[silverback]

I have used the Devcon before, but was unable to find any near by. I did find this:



Which is solvent based and should work to weld stuff back together. On the panel which has the J nut, I have backed it with an additional piece of plastic for structural support:




I will fill with some epoxy putty to regain the shape. Maybe some chopped fiberglass. I am tempted to lay an additional layer of glass on the back.

For the fairing, I have welded a couple of the pieces back together:




I am strongly considering a trip to the hobby shop for some unidirectional carbon fiber tape and good cyanoacrilate to back this. Usually, this can be laid down with less than 0.010" thickness. We'll see. I am not horribly concerned about looks, as the gash on the side the previous owner put in it still outshines the crack repair.

Wish me luck.

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[Bust]

Ah hell! I thought you were concerned about the outward appearance.
For the hidden spring nut area welding is good, as is for the outer stuff.

I was just looking at "keeping up appearances"
Way too much work screwing around with adhesives if ya ain't worried about final finish.

[tominca]

Small cracks in ABS plastics can be fixed by using ABS cement on the back side and working it into the cracks. ABS cement actually melts some of the plastic and when it hardens, the whole thing is bonded. I have used it in the top panel bolt hole tabs, and have repaired top cases and other ABS materials. Lots easier than learning ABS welding, and it should work fine for these small defects.

[silverback]

I found out the polypropylene plastic is impervious to the solvent in the glue. However, it did a fine job of making a very smooth repair on the back of the panel. It then came off clean. Thus, this part should have no stress risers to create more cracks which is a normal problem in a repair.

The back of the black panel is marked AES, which I assume is AmylEthylStyrene. I am going to look for some type of styrene to grind up and use as a filler and melt into the voids around the bolt hole. I think some carbon fiber uni-tape across the back will help with the strength.

TominCA: Is this ABS glue the same stuff used for ABS pipe in plumbing?

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[rushes]

I've always used MEK to repair ABS. (methyl ethyl ketone) You can buy it in the paint section at the local hardware store.
It melts it back together and then evaporates. I'm guessing it would work on any styrene?
It's as thin as water, so apply sparingly with a small brush.
You can use other broken pieces of ABS to make patch panels for extra strength.

[silverback]

I have been finding it very tough to find spare pieces of ABS. Any type of styrene is tough to come by, with the exception of expanded PolyStyrene (Styrofoam). You'd think there would be all kinds of stuff made from it, but I am not finding anything disposable that is.

I do know what MEK is, and I will look for some of it. I used to use a lot of it when working in the airport shop for cleaning parts and such. I do remember it would etch raw aluminum so I imagine it will melt about any kind of plastic. Its very volatile stuff.

I found some carbon fiber uni-tape today, and have put a single ply on the back of the black panel. I used some CA glue designed for plastics the hobby shop had. I don't know how well it will bond. I think I will look for some of the Devcon epoxy mentioned before or some of the ABS glue. I need something with a bit of body and working time. The CA glue made a mess of the fibers when I tried to apply pressure. I will end up sanding this off and trying again.

FWIW, the carbon fiber was $6 for enough to repair about 20 breaks like I have. Its made by Dave Brown Products and is the lighter weight stuff.

Thanks all for the great ideas. Real confidence boosters. I will keep trying and report progress.

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[garauld]

I have successfully welded a number of abs FJR pieces. My technique is: use a dremel and v-groove out the crack. Use a soldering iron to melt and fuse both sides of the crack back together. Melt ABS filler rod back into the grooved area to build it back up to beyond the surface. File and sand piece back to level. Repaint part. I have rod here and could send a few pieces at no charge if you PM me your address. The fix is actually quite easy to perform.

[bigjohnsd]

I've had good results (luck?) using a product called Valco HV-350. We used this in my shop to repair all manners of plastic parts from Styrene, ABS, ATV Fenders etc.... it hardens but remains flexible, can be sanded and painted. One of my techs had an old R-6 that I'd swear was more HV-350 than original body panels. Can buy it on Amazon, comes in a tube, splurge and buy their applicator, it really helps get all the material out of the tube.

[tominca]

I found out the polypropylene plastic is impervious to the solvent in the glue. However, it did a fine job of making a very smooth repair on the back of the panel. It then came off clean. Thus, this part should have no stress risers to create more cracks which is a normal problem in a repair.

The back of the black panel is marked AES, which I assume is AmylEthylStyrene. I am going to look for some type of styrene to grind up and use as a filler and melt into the voids around the bolt hole. I think some carbon fiber uni-tape across the back will help with the strength.

TominCA: Is this ABS glue the same stuff used for ABS pipe in plumbing?

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Same stuff you buy at Home Depot or other hardware or plumbing stores. I have repaired damaged saddlebags, top-cases and access panels on the FJR. Have not tried it on the main cowlings. ABS provides both solvent and filler in one. It will make a mess if you get carried away, but it will bond permanently, just remember it doesn't gain full strength for as much as a couple days.

[silverback]

I finally ended up using some CA glue from the hobby shop that is designed for plastic..."+fingernails" whatever the hell that means. It has a brush in it which makes application easier than the normal routine of gluing everything but your intended targets together. No kidding, last time I used CA glue, some how a leprechaun ended up glued to a wolverine's ass. Anyway...

I layered up about four plies of the unitape in various directions on each part. I surrounded the hole on the fairing and just covered it on the black piece. On the black piece, I filled the top side with epoxy and drilled the hole out again. Replaced the J-nut, and reassembled everything.

The repair held through the KC trip and no additional fatigue cracks have occurred. It appears to be as strong or stronger than the original pieces. Although, the looks aren't 100%. It could probably be touched up with some of that nail polish kind of touch up paint, but my colorblindness is prohibitive to matching colors well.

Other than that I could repaint the panel, but I suck at professional painting.

I'm just happy the thing isn't getting worse.

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[HotRodZilla]

I feel bad for the wolverine, but that dammed Leprechaun had it coming. Good ideas on the fix.

[Bust]

Fuk u dillo fuker...
As a "trained professional" in that field of endeavor I wasn't going too far in my suggestion regarding "proper" repair. You know where trained advice gets you.

Fuked in the ass by somebody smarter.

I knew even if I said the "Instructed" right way, somebody would come along with a better idea... And they might be right.
Just because I was taught to do it this way, don't mean new shit isn't bedder.

Gotta luv the interwebs for this.

[bluesdog]

I feel bad for the wolverine, but that dammed Leprechaun had it coming.

Gotta be quote of the day.

May we please have a like button?

[HotRodZilla]

Fuk u dillo fuker...
As a "trained professional" in that field of endeavor I wasn't going too far in my suggestion regarding "proper" repair. You know where trained advice gets you.

Fuked in the ass by somebody smarter.

I knew even if I said the "Instructed" right way, somebody would come along with a better idea... And they might be right.
Just because I was taught to do it this way, don't mean new shit isn't bedder.

Gotta luv the interwebs for this.

Oh, it's ok sensitive boy. I liked your ideas too. It's just that I have no idea how to fix FUBAR'd plastic, so seeing this stuff is cool. It puts little ideas in my baby sized tool box.

Old guys are good at fixing shit. One day, I'll be an old guy, son I better pay attention now and represent!!

[Bust]

Thanks for the mangina balm flea dik.. I feel all bedder now.

[silverback]

Fuk u dillo fuker...
As a "trained professional" in that field of endeavor I wasn't going too far in my suggestion regarding "proper" repair. You know where trained advice gets you.

Fuked in the ass by somebody smarter.

I knew even if I said the "Instructed" right way, somebody would come along with a better idea... And they might be right.
Just because I was taught to do it this way, don't mean new shit isn't bedder.

Gotta luv the interwebs for this.

I tried to source plastic rod locally. No joy. Garauld offered to mail some, which I appreciate, but I used to own a heat gun with a nozzle that was made to weld plastic. Never was any good at it. I think it would have turned into buying a new panel...

Next time, I'll be sure to invite you for the expertise, tooling, and I'll buy the cheap beer and supply insults.

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